In recent years, the progress of downsizing and lightening of electronic equipments is remarkable, and with this, requirements for downsizing and lightening of batteries used as power sources for driving the electronic equipments have also much more increased. In order to meet such requirements for downsizing and lightening, a nonaqueous electrolyte secondary battery, such as a lithium ion secondary battery, has been developed as an electric storage device. Further, as an electric storage device having properties such as high output density and favorable cycle performance, an electric double layer capacitor is known. Furthermore, as an electric storage device meeting uses requiring high energy density property and high output property, a lithium ion capacitor wherein electric storage principals of a lithium ion secondary battery and an electric double layer capacitor are combined is known.
As negative electrode materials used for such electric storage devices, carbon particles such as graphite particles have been used for, for example, a lithium ion secondary battery. However, with the aim of further increase in capacity, a composite material of carbon and silicon has been studied. For example, in a patent literature 1, a lithium ion secondary battery containing carbonaceous particles obtained by calcining a mixture of a silicon precursor such as polyethoxysilane and a carbon precursor such as a furan resin, pulverizing the calcined product to prepare silicon-containing carbonaceous particles, coating the particles with a carbon precursor such as coal tar pitch and then calcining the carbon precursor is described. In a patent literature 2, a lithium ion secondary battery containing a composite electrode material obtained by adding a mixture of a carbon precursor organic polymer compound such as a furan resin and an organosilicon compound such as a tetramethoxysilane partial condensate to graphite particles and calcining the resulting mixture is described.